In connection with motor vehicles, the driver needs to be able to steer the vehicle in a simple way. To this end, motor vehicles are traditionally equipped with some type of steering arrangement, for example a vehicle steering wheel having a steering wheel ring connected to a steering wheel center via steering wheel spokes and which is arranged at right angles on a steering main shaft.
Such a steering wheel can be arranged in the vehicle in different ways. For example, the steering wheel in a vehicle of the private car type is usually arranged in front of the driver seat essentially vertically, the extension of the steering wheel ring coinciding with a plane essentially at right angles to the floor of the vehicle. In vehicles of the heavy-duty vehicle type, on the other hand, the steering wheel is usually arranged in front of the driver seat essentially horizontally, the extension of the steering wheel ring coinciding with a plane essentially parallel to the floor of the vehicle.
In the event of a collision, the driver is thrown forward in the vehicle, in the direction of the steering wheel. With a steering wheel of the heavy-duty vehicle type, the body of the driver strikes the steering wheel (the steering wheel ring, from the side in the radial direction of the steering wheel) and the steering wheel ring is deformed while absorbing energy.
One problem with an arrangement of the above type arises in vehicles of the heavy-duty vehicle type where the steering wheel usually has a great steering wheel deflection, for example 3.5 turns for full steering wheel deflection in each direction. This means that even a relatively small turning movement of the wheels, for example a deflection of the wheels in connection with a vehicle collision, results in the steering wheel starting to rotate, which can in turn lead to the protruding parts of the deformed steering wheel ring causing injury to the driver.
Even in cases when the steering wheel is equipped with an airbag, it can happen that the driver still strikes the steering wheel when a collision occurs. This can occur, for example, in the final stage of a collision sequence (which may be up to ten seconds in the case of heavy-duty vehicles) after the airbag has been emptied of the inflating gas.
Another problem in heavy-duty vehicles is that the steering wheel has to be sufficiently torsionally rigid in order to withstand the stresses which arise in the steering wheel if the steering servo should cease to function (the power steering fails) and the driver has to steer the vehicle without power assistance. The steering wheel also has to stand up to bending forces that arise on the steering wheel as a result of the driver making frequent use of it as a support when climbing into the vehicle.